As a wireless communication service is centered on data transmission, a transmitter and a receiver process a high Peak to Average Power Ratio (PAPR) and broadband data with high efficiency and high linearity. In a Frequency Division Duplex (FDD) system that transmits and receives data at the same time, noise of a power amplifier can flow into a receive frequency band and thus degrade reception. Hence, low output noise of the power amplifier is desired in a receive band (RX band noise). For doing so, a current common power amplifier (e.g., a single amplifier or a multi-mode multi-band amplifier) obtains linearity through an efficient back-off using a fixed power supply. The current common power amplifier operates in a back-off region. Accordingly, the power noise does not affect the output of the power amplifier owing to a gain of low voltage variation (hereafter, referred to as a VcctoRF gain) or a high Power Supply Rejection Ratio (PSRR).
However, a related-art method using the fixed power supply operates in the back-off region and emits heat from a high supply voltage even when the output signal is weak, thus limiting efficiency. To address this, an envelope tracking power amplifier can be used. Envelope tracking power amplification can achieve high efficiency by changing a supply voltage according to the output power and ultimately reducing power loss in the power amplifier operation.
FIG. 1 illustrates an envelope tracking power amplifier according to the related art. Referring to FIG. 1, the envelope tracking power amplifier includes a baseband signal processor 110, a supply modulator (SM) 120, a Radio Frequency (RF) processor 130, and a power amplifier 140. The baseband signal processor 110 generates, up-converts, and outputs IQ data in an RF frequency. The SM 120 receives a signal from the baseband signal processor 110 and outputs the same envelope as an input envelope. The RF processor 130 converts the IQ data fed from the baseband signal processor 110 to an RF signal and provides the RF signal as an input signal of the power amplifier 140. The power amplifier 140 amplifies and outputs the input signal fed from the RF processor 130 using the supply voltage from the SM 120.
The envelope tracking power amplifier separates an envelope component of the signal applied to the input and then changes the amplifier supply voltage by tracking the component. Since the envelope power amplifier operates in every instantaneous saturation region compared to a general power amplifier applying a constant supply voltage, the envelope power amplifier can achieve high efficiency.
An SM supplies the power to the power amplifier according to the envelope. Since the envelope tracking power amplification operates the amplifier in the saturation region to raise the efficiency, the VcctoRF gain characteristic of the power amplifier increases compared to the related-art fixed voltage. That is, in the envelope tracking power amplifier, not only the noise of the power amplifier but also the noise of the SM affect the output.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.